This invention relates to a microwave seal structure in a microwave heating apparatus such as a microwave oven for preventing leakage of the microwave energy through the gap between the door and the heating chamber of the microwave heating apparatus, and more particularly to improvements in the door seal structure in a microwave heating apparatus of a type in which an electric heater is provided in combination with a microwave generator.
A known microwave heating apparatus of the type provided with an electric heater in combination with its microwve generator is also capable of performing the function of pyrolitic self-cleaning. In such a microwave heating apparatus, the internal temperature of the heating chamber is generally raised to about 500.degree. C. during self-cleaning, and therefore, the door is generally provided with a thickness that is considerably greater than an ordinary oven door due to the requirement for better heat insulation capability of the door.
In a microwave heating apparatus of the kind described above, a microwave seal structure having a choke arrangement with a configuration such that it can be received in the heating chamber in the closed position of the door is most frequently used in practice so that the microwave seal structure can be well matched to the thick door of the microwave heating apparatus. Further, in order to improve the microwave seal performance of the seal structure in a microwave heating apparatus of the kind described above, a plurality of slits are provided in the wall portion extending towards the inlet of the choke cavity among the wall portions defining the choke cavity. Such an arrangement is disclosed, for example, in U.S. Pat. No. 3,767,884 to Osepchuk et al., issued Oct. 23, 1973. The disclosure of this patent is incorporated by reference herein and reference is to be made thereto for details of the prior art construction. It is well known that the size of the gap between this slitted wall of the choke cavity and the corresponding portion of the walls defining the heating chamber exerts a great influence on the microwave seal performance of the choke and is desirably as small as possible from the viewpoint of microwave seal performance. However, it is difficult to maintain the surface flatness of the wall of the choke cavity formed with the slits, because this wall is finely divided by the slits. A temperature as high as about 800.degree. C. is generally applied to the walls when the walls are subjected to a finishing treatment such as finishing with enamel. Since the slitted wall of the choke cavity will be greatly deformed in such a case, the slitted wall of the choke cavity may finally make contact with the opposite wall portion of the heating chamber unless the gap therebetween is designed to be much larger than when the wall of the choke cavity is not provided with any slits. However, provision of a very large gap between the slitted wall of the choke cavity and the opposite wall portion of the heating chamber has inevitably resulted in an objectionable increase in the amount of leakage of the microwave energy, as pointed out hereinbefore.
It is therefore a primary object of the present invention to provide an improved door seal structure which obviates the aforementioned defects of the prior art structure in both quality and performance in spite of the fact that it is quite simple in construction.